1. Technical Field
The present invention relates to an ultrasonic sensor and a manufacturing method for the ultrasonic sensor.
2. Related Art
In the related art, there is an ultrasonic sensor in which electromechanical conversion characteristics of a piezoelectric element are employed. For example, there is an ultrasonic sensor that includes a support member (a substrate disposed across an XY plane formed by an X axis and a Y axis), a movable film (vibrating plate) provided on the substrate, an electromechanical conversion element (piezoelectric element) provided on the vibrating plate, and an opening (space) formed in the substrate on a side of the vibrating plate, which is opposite to the piezoelectric element (see JP-A-2011-255024 (paragraph [0047], FIG. 5, and the like) and JP-A-2011-259274 (paragraph [0044], FIG. 5, and the like)). In both JP-A-2011-255024 and JP-A-2011-259274, ultrasonic sensor elements that include the piezoelectric element, the vibrating plate, and the space, as described above, are adjacent at regular intervals so as to form a lattice extending along the X-axis and the Y-axis.
In this type of ultrasonic sensor, an ultrasonic wave is transmitted and received in response to displacement of the piezoelectric element of the ultrasonic sensor element. The possibility to enhance displacement characteristics of the piezoelectric element is useful for enhancing the efficiency of transmission and reception of the ultrasonic wave and, eventually, for enhancing the sonic characteristics.
However, in recent years, there has been a demand for ultrasonic sensor elements having a high-density arrangement; on the other hand, in JP-A-2011-255024 and JP-A-2011-259274, a problem arises in that it is difficult to maintain good sonic characteristics while achieving a high-density arrangement of the ultrasonic sensor elements.
In other words, in JP-A-2011-255024 and JP-A-2011-259274, since the ultrasonic sensor elements are adjacent at regular intervals so as to form a lattice extending in the X-axis direction and the Y-axis direction, it is not possible to ensure a sufficient wall thickness for the space in the ultrasonic sensor element. In this case, the entire substrate is likely to be influenced by the displacement of individual piezoelectric elements and, thus, there is a possibility that the displacement of individual piezoelectric elements will cause overall bending (structural crosstalk) of the vibrating plate.
When the occurrence of the structural crosstalk described above causes variation in the displacement characteristics of the individual piezoelectric elements, the efficiency in the displacement of the entire piezoelectric elements thus deteriorates and, as a result, the sonic characteristics are likely to deteriorate. Such problems arise not only in the ultrasonic sensors disclosed in JP-A-2011-255024 and JP-A-2011-259274, but also in ultrasonic sensors in which electromechanical conversion characteristics of the piezoelectric element are employed.